By geometrical optics, an ideal dish antenna requires a parabolic reflector, and a point radiation source at the focal point of the reflector. Such an antenna has gain (directivity) that is proportional to its diameter when illuminated properly. However, in practice the bandwidth and power handling of a high-gain dish antenna is dependent on the bandwidth and power handling of its respective feed element. This is particularly true at the low end of the frequency range. For many dish antennas, the lowest operational frequency can be determined by the dish diameter. For this invention, the dish diameter is only limited by operational constraints. The bandwidth of the dish can also be limited by the bandwidth of the feed element. The feeds for such high-power, high-gain, very broadband dish antennas must meet several requirements. First, the feed design must meet the bandwidth requirements. Second, the feed design must have minimum variation of the location of its phase center in respect to the focal point of the dish over the entire design bandwidth (a constant phase center). Third, the width of the beam pattern must match the dish size over the entire desired frequency range. Fourth, the feed must be able to transmit at the required power levels.
Several types of feed antennas have been researched. A flat exponential spiral feed element may have a wide bandwidth and a constant fixed phase center, however the radiated pattern will be circular and not linear. A printed circuit board spiral antenna may not meet the high power handling requirements. Also, the spiral antenna can have a very broad antenna pattern, which can cause the illuminated area to be larger than the dish size for the desired frequency of operation. Log periodic feed elements can have non-constant phase centers, which can result in a variation of the focus of the dish with frequency. Dish antennas with a waveguide feed design can be limited by the single mode bandwidth of the waveguide (i.e. the antennas do not have a wide bandwidth). Horn antennas can have constant phase centers; but, at the lowest frequencies of operation they may have a large physical size and can block a significant portion of the center of the dish, reducing the effective aperture and gain.
In view of the above, it is an objective of the present invention to provide a tapered slot feed for a dish antenna that can operate satisfactorily over a very wide bandwidth. Another objective of the present invention is to provide a tapered slot feed for a dish antenna that operates with a relatively constant fixed phase center over the entire bandwidth of operation. An additional object of the present invention is to provide a antenna having a tapered slot feed that allows for a combination of high power handling and very wide frequency band width, when compared to the feed elements in the prior art. Still another objective of the present invention is to provide a tapered slot feed for a dish antenna with a beam pattern that matches the dish size over a wide range of operation. Yet another object of the present invention is to provide a tapered slot feed for a dish antenna that can operate in a continuous wave mode at high power.